Method of recovering lead-tin alloys



,Patented Jan.- 1.9,l 1932 UNITED STATES PATENT 4ol-Flc'lI EDWARD FRANK KERN, E NEW YoEK, N. Y., AssieNoR 'ro AMERICAN METAL coM- rANY, LIMITED, or NEW YORK, N. Y., A' CORPORATION 0E NEW Yom:

METHOD or EEcovEErNe LEAD-TIN ALLoYs Application led January .29, 1929. Serial No. 335,938.

ing metals in the form of alloys and mix-- tures are available. This material is derived from secondary white metal alloys, from the smelting of lead-tin ores and metallurgical by-products and from Athe refining of lead 'and tin and of lead-tin alloys. This mate- M1 5 rial, containing alloys of lead and tin, with various impurities including zinc, iron, nick- 'e'l,i'r"antimony, arsenic, bismuth, copper, sulfr, silver and gold -is substantially useless because no practicable metlmd of separating v5*-0 the impurities and recoverin 'the lead-tin t tion and any which can be produced in re alloys has been devised hereto ore.

'It is the primary object of the present in'- ve'ntion to recover lead-tin alloys substantially free from impurities and to obtain at the same time the various elements present as impurities in the alloys treated in an economical and commercially .feasible manner.

' The invention depends upon the discovery that the lead-tin alloys can be separatedreadily from many of the metals which are mingled in the `scrap material by liquation, and that the impure lead-tin alloys thus secured may be separated, provided that the impurities are restricted within certain limits, in a substantially pure condition by ele trolyzing under the conditions/hereinafter described. The lead-tin alloy is deposited upon the cathode, whereas the impurities are retained in the residue which can be separately treated to recover certain valuable elementstherein..

Thus if the raw material includes such elements as zinc, iron, nickel and copper, it is treated preliminarily by liquation at a suitable temperature, so that theilead-tin alloys separate, leaving a residual dross containing most of the impurities. .This initial separation should be so conducted as to permit the separation of a lead-tin alloyV containing less 5 than 10% of impurities, a result which can be attained ordinarily by heating the raw material at a' temperature of between 300 which is melted at that temperaturefrom the residual dross. If the liquated lead-tin alloy 4and 4000 C. and withdrawing the metal r contains more than 10% of impurities, it can l be diluted by a suitable proportion of a'purer lead-tin alloy -to bring the percentage of impurities below the limit mentioned.

The liquated lead-tin alloy may contain a proportion-of copper, if copper is present in the raw material. If` the copperv exceeds 0.5%, it should be removed by heating the lead-tin alloy to about 310 to 315 Cl and introducing to the molten alloy about one paund of sulfur per pound of copper to be removed. The dross is skimmed from the metal which is then heated to about 350 C.

and cast into anodes.

The residual dross. from the initial liquamoving copper from the lead-tin alloy are then oxidized and resmelted to`remove' the major portion of the arsenic, sulfur and iron and apart of the antimony which ma)7 be present in .combinations'such as FeSSn, Fe-

cathode material.

a lower proportion of impurities or use in preparing-the lead-tin anodes vwhich are subsequently electrolyzed'- to produce substantiallygpure lead-tin alloy The electrolysis 'of the lead-tin alloy an'- .Y odes must be .conducted under carefully reg-:'19

ulated conditions. As an electrolyte, I prefer to employ solutions containing lead and tin fluosilicates and free fluosilicic acid,

lead and tin uoborates and free fluoboric acid, or lead and tin cresol sulphonatev and free cresol sulphonic acid, or mixtures of such solutions. The electrolyte should include approximately 50 to 125 grams of lead and tinl per litery as soluble salts and from 30 to 80 i grams per liter of free acid, the specilic gravity of the electrolyte ranging from about 1.15

to 1.35. Electrolysis is conducted at a temperature between 40 and 50 C. with electrode current densities of from 10 to 25 aIn` peres per square foot. The lead-tin alloy is dissolved at the anode and deposited'at the cathode substantially free from impurities, and the cathode material can be melted and cast into commercial bars.

In order to effect'the separation' of the lead-tin alloy in a dense mass on the cathode, it has been found desirable to add to the electrolyte an organic reagent such as gelatin or glue or mixtures of either gelatin or glue with cresol. The amount of the organic addition reagent s'uchas gelatin or glue required is about one part by weight to three thousand parts by Weight of the electrolyte. The organic addition reagent should be added periodically to the electrolyte as indicated by the characteristic form of the cathode deposit. The organic addition reagents mentioned are merely illustrative, and other .reagents adapted to produce the same or similar results with -respect to the density of the cathode deposits canbe employed.

To ensure continuity and satisfactory operation of the electrolysis, it is essential to circulate the electrolyte from the bath in which electrolysis is conducted to a precipitating tank in which the electrolyte. is' brought into contact withgranulated leadtin alloy. The circulation should be conducted at the rate of about one gallon per minute per thousand amperes of current flowing. The circulation and the vcontact with the granulated lead-tin alloy precipitate the impurities which are dissolved in the 'electrolyte from the anode residues and replaces the lead and tin which are lost as occluded electrolyte in the anode residues and by spillage and leakage of the electrolyte. The concentration of the electrolyte in lead and tin, which is an essential condition for successful operation, is thus maintained substantially constant.

The loss of electrolyte by occlusion in the anode residues and byleakage and spillage averages about 10 pounds per ton of anodes refined for each per cent of impurities that the anodes contain, provided that the anode residues are properly washed and care is taken to`prevent excessive losses by spillage and leakage. There is, therefore, a certain loss of acid, and since the concentration of the acid in the electrolyte isan essential condition, it is necessary to add acid from time to time to the electrolyte to make up such losses.

Under the conditions defined and particularly the maintenance of these conditions Without substantial variation, it is possible to continuously separate a substantially pure lead-tin alloy at the cathode. y

In carrying out the invention there is a proportion of anode sorap'as well as insolublel 1,84a',oas

\ anode residues which accumulate; The

'scrap is washed to remove the anode residues and to recover theelectrolyte. The scrap after washing is remelted into anodes. The residues are filtered and washed to separate the electrolyte which is returned to the circulating tank and mingled with the electrolyte which, after passing over the granulated lead-tin alloy, is returned to the electrolytic bath. The relatively weak wash solutionsmay be evaporated'to a specific gravity of about 1.25 before they are introduced to the electrolyte). The washed anode residues,Y

drawing, which is a flow sheet representing the procedure.

The raw material, consisting of lead-tin alloys from various sources a'nd with impurities l such as those hereinbefore mentioned, is liquated in a reverberatory furnace or melting kettle indicated at 5, at a temperature between 300 and 400 C. The molten leadtin alloy separates and leaves the residual dross. The latter is withdrawn and is oxidizedand smelted in a reverberatory furnace indicated at 6, Impurities such as arsenic, sulfur, iron, and antimony are thus removed, and the resulting impure lead-tin alloy indicated at 7 is returned and mixed with the raw material. If the liquated lead-tin alloy contains more than 10% of impurities, a purer alloy from any suitable source is mixed therewith or the liquation may be repeated in the reverberatory furnace 5 to produce a purer material.

The liquated lead-tin alloy containing less than 10% of impurities is then melted if it contains more than 0.5% of copper in a kettleA or furnace indicated at 8, and sufficient sulfur is added when the metal'is at 'a temperature of about 315 C. The sulfur combines with the copper and the resulting dross is skimmed from the' metal. It may be mixed withthe dross in the furnace 6 and liquated and oxidized therewith. The metal in the kettle or furnace 8 is then heated to about 350 C. and is cast at a temperature between 300 and 350 C. in the form of lead-tin anodes 9 adapted for use in the electrolytic tankA 10.

The electrolytic tank is supplied with an electrolyte containing between 50 and 125 grams per liter of lead and tin as soluble salts and from 30 to 80 grams per liter of free acid. The salts and acids used are preferably those hereinbefore mentioned. This electrolyte isl circulated constantly between the electrolyticl l'tank 10 Vand a' precipitating tank 11 which contains a quantity of granulated lead-tin alloy. The circulation is maintained at a rate of about one gallon 'per' minute per thousand amperes used.

Electrolysis is conducted in the electro- ,lytic tank at a temperature of about 40 to 50 C. with electrode' current densities between. 10 and 25 amperes per square foot,

added from time to time to replace that lost in the anode residue and by leakage and spilla e. l

gThepure lead-tin cathodes removed from the bath are melted in a furnace 12 and cast into commercial bars. The lead-tin alloy thus recovered is suitable for numerous commercial uses,.being substantiallyY free from impurities which would seriously aifect the qualit-yl of the metal.

The anode scrap and the anode residues are removed from the electrolyte and washed at 13. The anode scrapis then remeltedA at -14 and returned in the form of fresh anodes to the electrolyte. The anode residues are filtered and-washed at 15, the electrolyte recovered being returned directly to the tank 11. The weak wash solutions are evaporated at 16 and the concentrated solution is then delivered to the tank 11.

The operation as described involves the substantially complete utilization of the raw material and the recovery therefrom in particular of commercial lead-tin alloys constituting the most valuable portion of the raw scrap material. The operation isreadlly controlled and can be carried out economically and efficiently. The method .af-

4vsus fords, therefore, a practicable procedure whereby scrap material is converted into valuable commercial products. Various changes may be made in the details of the method as described especially to accommodate the operation of the differing compositions of the raw materials treated without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of recovering lead-tinalloys which comprises electrolyzing anodes "consisting of impure alloys of lead and tin in a bath containing from 50 to 125 grams of soluble salts of lead and tin and from 30 to 80 grams of free aid ger liter of'electrolyte.

2. The method of'recovering lead-tin ali loys which comprises electrolyzing anodes of lead and tin containing not more than 10% of impurities in a bath containing from 50 to 125 grams of soluble salts of lead and tin and from 30 to 80 grams of free acid per liter of electrolyte.

3. The method of recovering lead-tin alloys which comprises electrolyzing anodes l vconsisting of impure alloys of lead and tin in a bath-containi11g-from 50 to 125/grams of solublesalts of lead and tin and from 30 to 80 grams offree acid lyte, and continuously circulating the electrolyte between the electrolytic bath and a body of lead tin alloy to precipitate dissolved impurities and to maintain the concentration of lead and tin therein. v

r liter of electro- 4. The method of recovering lead-tinalloys which comprises electrolyzing anodes of lead and tin containing not more than 10% of im'- Vpurities in a bath containing from 50 to 125 grams of soluble salts of lead and tin and from 30 to 80 grams of free acid per liter of electrolyte and continuously circulating the electrolyte between the electrolytic. bath and of free acid per liter of electrolyte.

' 6. The method of recovering lead-tin alloys from scrap material which comprises liquating the material to separate impure leadtin alloy therefrom, addingl sulfur to the molten alloy to remove copper therefrom,' and electrolyzing anodes of such alloy in a bath containing from 50 to 125 grams of soluble salts of lead and tin and from`30 to 80 grams of free acid per liter of electrolyte.

7. The method of recovering lead-tin alloys from scrap material which comprises'liquat-R ing the material to lseparate impurev leadtin alloy therefrom, electrolyzing anodes of such alloy containing not more than ten per l cent of impurities in a bath contaning from 50 to'125 grams ofrsoluble salts of lead and tin and from 30 to 8O grams` of free acid per liter of electrolyte, and continuously circulatingv the electrolyte between the electrolytic bath and a` body of lead-tin alloy to precipitate dissolved impurities and to maintain the concentration of lead and tin therein. l

8. The method of recovering lead-tin alloys .from scrap material which comprises liquating the material to separate lmpure leadtin alloy therefrom and electrolyzing anodes of such alloy in a bath containing from 50 to 125 grams of soluble salts of lead and tin and from 30 to 8 0 of electrolyte.

9. The method of recovering lead-tin alloys grams of free acid per liter from scrap material which comprises liquating the material to separate impure leadtin alloy therefrom, adding lead-tin allo)T containing a low proportion of impurities to i of e1ectrolyte,'and continuously circulating reduce the total impurities below 10%, and electrolyzin anodes of such alloy in a bath containing rom 50 to 125 grams of soluable salts of lead and tin and from 30 to 80 grams of free acid per liter of electrolyte.

. 10. The method of recovering ,lead-tin alloys from scrap material which 4comprises liquating the material to separate impure lead-tin alloy therefrom, electrolyzing anodes of such alloy in a bath containing from 50 to rams of soluble salts of lead and tin and rom 30 to 80 grams of free acid per liter the electrolyte between the electrolytic bath and a body of lead-tin alloy to precipitate dissolved impurities and to maintain the concentration of lead and tin therein.

11. The method of recovering lead-tin alloys from scrap material which comprises liquating the material to separate impure lead-tin alloy therefrom and electrolyzing anodes of such alloy containing not more than 10% of impurities in a bath containin from 50 to 125 grams of soluble salts of le and tin and from 30 to 80 grams of free acid per liter of electrolyte.

In testimony whereof I aix my si nature.

EDWARD FRANK K RN. 

